Process for producing ketene



' IN1/ENT ATTORNEY C H GREENEWALT F 1 d o t 25 1933 Sg g v i V Sept.8 1936 Patented Sepe 8, 1936 UNITED STATES PATENT OFFICE 4PROCESS FOR PBODUCING tion of Delaware application october zs, 193s, serial No. ses.

s mm. (ci. zoo- 123) Ihis invention relates' to an improved process for the manufacture ot keteneand more particularly to a process for improving the yield ot ketene as made by the pyrolysis ot ketene-iorming sub- 5 stances such as acetone.

The manufacture of ketene by Pyrlysis of acetone is a well known process. An improved method of carrying out the pyrolysis at'very high tem peratures with very short times oi' contact is disclosed in the copending application ot George D.

Graves and C. H. Greenewalt. Serial No. 618,702, med June '22/32. It has been found that subsequent losses of ketene may-eqme about through the polymerization o! the ketene as it is dissolved l5 by unconverted acetone, condensed from the eiliuent gases. These losses may -besubstantial but may be avoided by the process ot the-present invention.

Thls invention has as an object the production of ketens in hiah yields by the pyrolysls .ot ace.

tone. A further object is the recovery, without los of ketene. ci imconverted acetone from the Pyrolysis productsso that it can be returned to 'the pyrolysis tube for re-use.

The obiects are'aed by the f ollow.

ing invention wherein the pyrolysis con' taining ketene and the ketene-torming substance such as acetone areflrstpassedthrough apre,- cooier or heat-exchanger in which the pyrolysis vapors'are brought approximately to their dewpoint. and. second through a means arranged so that the condensed ketene-iorming substance ilows downward into the warm none-- counter-current to the incoming vapors. The

ketene forming substance is thus'condensed and the ketene removedl as a vapor. the loss of ketene by solution in the ketene-formin'g substance and subsequent polymerization being avoided.

Various substances may be pyrolyaed to yield 40 ketene. Acetic acid. acetic anhydride, acetaldehyde. and acetone may be thus employed. The preferred substance is. however; acetone. This is pyrolyaedby anyofthe methods know'ninthe art including that oithe copending .Graves and Greenewalt application above described.

-The pyrolysis vapors issuing trom the high temperature zone are cooled to approximately their dew-point in any desired manner. The vapors at their dewpoint are then admitted to a redux condenser capable of returning the maior poracetonev in the receiving vessel is either drawn of! or held at about 56 C. in order to discharge any residual dissolved ketene and to prevent the solution o! any appreciable amount ot ketene from the vapor space. The acetone which is essentially at its boiling point may be allowed to run continuouslvtrom this receiver to a dia-- tilling column. from the top ot which may -bo taken recovered acetone suitable for reaction in the process. and from the bottom of which may berecovered any. small amounts of acetic acid or acetic anhydride which may result trom water in thel original acetone .or fromside reactions. The material thus condensed contains a negligible amount ot ketens polymer. The uncondensed gases issuing from the top o! the redux condenser willcontainallottheoriginalketeneandlnl! be treated in any desired manner.

The invention. therefore, comprises lowing steps.

L'Ihepyrolysisvaporscontainingketeneare cooled to approximately their dew-point. By dew-point is meant that temperature at which theiirstdropot condensate forms. l

1I. The vapors 'at their dew-point are admitted tothebottomoiareiluxcondenserwhichreturns the maior'portion of the unconverted acetone assliquidtoareceiver below the condenserandpasses' substantiallysllottheketenciosuitableabmtion apparatus designed for itsutilization.

Thereiluxcondensation oftheacetoneisthe most importantand really essential step in carrying out the present invention since the liquid being returned down the condensing surface 'continuously meets ascending warm .vapors which strlp out ketene and permits it to remain in solutionforonlyaverysmallincrementoftime.

Theliquid'leaving thebottomofthereiluxcom' denser is thus rendered substantially free o! d issolved ketene.a nd the maior portion of the ketone' passes from the top oi' the condenser. Thisarrangement eliects in essence a vapor phase sepa- 'ration of-acetone from ketene. in which phase` there is substantially no polymerization of ketone. Themaintenanceoftheacetoneinthereceiver underthecondenseratorneartheboilingpoint oi the acetone in order to prevent condensation oi acetone prior to the entrance of the pyrolysis vapors into the reiluxis a desirable refinement in theprocesssinoebytheuseofthissteptherels substantially no loss oi' ketene through solution in the recovered acetone and subsequent polymerization.

The recovered acetone at or near its boiling point may be run from. the receiver continuously the roior discontinuously to a rectification column which separates pure recovered acetone from any high boiling constituents which may be present. These high boiling constituents are substantially free from ketene polymers and are negligible in quantity compared to the ketene produced.

The following example is given in illustration of the process of the present invention but is by no means to be regarded as limitative'. The numbers used in designating the apparatus refer to the corresponding numbers in the accompanying drawing.

Acetone from tank (I) for fresh acetone or tank (2) for recovered acetone is pumped by pump (3) at the rate of 75 cc. per minute through a Y. inch inside diameter copper tube (l), so placed in an electric furnace that 90 inches of the tubing lie within a zone between '160 and 810 C. The vapors issuing from the furnace are conducted through a coil (5) of 9S" copper tubing l5 feet long. held in a water bath maintained at a temperature which will cool the vapors to their dew-point or about 54 C. (Theoretically, the dew-point ranges from a temperature near the boiling point of ketene with 100% conversion to the boiling point of acetone with conversion. Actually, it is within a few degrees of the latter because the per cent conversion is usually small). The cooled vapors are admitted to a cylindrical copper vessel (1), 4 inches in diameter and 0 inches high, surmounted by a water-lacketed reflux condenser (6) 10 feethigh and l inch in diameter. Vessel (1) is connected to the recovered-acetone tank by a vent line (il). The condensed acetone, which is returned by the remn: condenserA to the cylindrical receiver beneath it. is held therein at about 56 by the application of h'eat to the receiver. .The condensed acetone,

essentially free from dissolved ketene. and substantially at its boiling point. is withdrawn continuously from an outlet located inches above the bottom of the re-boiler vsel. and allowed to flow to a rectifyingcolumn (ii),from the top of which acetone. substantially free from impin'ities, is withdrawn through a condenser (I2) for recirculation. A small still pot (II). beneath the rectincation column served to collect high boiling constituents which may be drawn oil' through pipe It is kept substantially free from acetone by the application of heat.`

The ketene. together' with gases resulting from the decomposition of ketene. and also a small amount oi' uncondensed acetone. from the top oi' the reflux condenser through pipe (i8) to the bottom of an abrption column (l). down which water is pumped from tank (9) through pump (lil) at a rate suilicient to absorb the ketene and convertit to acetic acid which flows continuously from the bottom of the absorption column and is stored in reservoir (il). Uncondensed vapors are passed through absorbers (i5) and vented through pipe (it). Absorbers (I5) are not essential.

The apparatus was operated as described for 154 minutes. It was then found.that the liquor produced in the absorption tower contained acetic acid equivalent to 21.7 mols of ketene. '111e residue withdrawn from the still beneath the acetone rectincation column was found to contain a small amount of acetic anhydride. together with some acetone. but essentially no ketene polymer. By deducting the amount of acetone recovered by distillation oi' the liquid products from the amount fed to the pyrolysis tube. it was round that 26.4 mois of acetone had been consumed.' Since 23.26 mois o! acetic acid were produced (21.7 as acetic acid, 1.56 as acetic anhydride as above indicated) the yield was 88.2%. 'I'he loss may be accounted lor as gaseous decomposition products of ketene.

The transformation of the ketene to acetic acid is merely one method of utilizing'A the ketene and is here adopted largely because it furnishes an easy method of determining the yield. The ketene may also be reacted with acetic acid, aniline, alcohols and the like.

The improved method for preventing loss ci ketone can be applied to any mixture of vapors obtained by pyrolysls oi acetone, acetaldehyde. acetic acid. acetic anhydride, or other ketene forming substances. 'I'he pyrolysis may be any of those disclosed in the prior art although the pyrolysis process of the above identified Graves and Greenewalt application gives improved yields.

Any desired means may be used for precociing the pyrolysis product issuing from the reaction tubefrom the high temperature of decomposition to the dew-point of the pyrolysis vapors. Water-coo1ed coils or any type of heatexchanger may be used, or a part of the cooling may be brought about by spraying an inert liquid such as acetone into the gas stream. There should be little or no actual condensation of acetone in this part of the process.

Any emciently operating reflux condenser will serve to separate the ketme from unchanged acetone without appreciable loss of ketene dissolved in the liquid condensate. A reflux condenser is particularly well adapted to this purpose because the liquid condensate is continuously stripped of ketene by the hot ascending vapors.

Through the use of this invention loss of ketene by polymerization to ketene dimer may be almost entirely eliminated. This loss has never been avoided in the prior art except in processes wherein the ketene is utilized practically immediately after formation, no condensation of acetone being permitted until the ketene has reacted. This latter exception requins a fractionation of large amounts of unchanged acetone from the reaction product as a separate step in the process. a step which is obviously disadvantageous. In the process of the present invention the acetone recovery is continuous. This continuous recovery minimizes the amount of acetone in process and permits the use of inexpensive recovery equipment. 'Ihere is an additional important advantage in the economy of heat since the acetone is fed to the rectification column essentially at its boiling point.

As many apparently widely dliferent embodiments of this invention may be made without' departing from the spirit and scope thereof. it is to be understood that I do not limit myself to the specific embodiments thereof except as defined in the appended claims.

l. In a process for the preparation of ketene by the pyrolysis of a ketene-iorming substance. the step which comprises leading the pyrolysis gases thru cooling-means to reduce their temperature to the dew point, then upward thru a reflux condenser whereby to effect substantially vapor phase separation of ketene from the ketene-forming substance. the condensed keteneforming substance being maintained at sub stantially its boiling point.

2. In a process for the preparation of ketene ketene, the condensed l (sans CRAWFORD mlLLocx GREENEVALT. 10

by the pyrolysis of acetone. the step which comprises passing pyroiysis gases cooled substantialiy to their dew point thru a reflux condenser counter-current .to a descending ilow oi( condensed acetone whereby to eiIect substantially vapor phase separation oi the acetone from the acetone being maintained substantially at its boiling point to prevent absorption of ketene therein.

3. In the process o! producing ketene by the cmarrnoi'r yel CORRECTION.

Patent No. 240525,286. September 8, 1.936.

CRAWFORD HALLOCK GBEENEWALT It is hereby certifiedtthat error appearsA in the printed specification oi the above-numbered patentrequiring correction as follows: Page 2. second column linel. for ketone read ketene; and i shouldbe read with this correction therein that the same may conform to the record of the .case in' the Patent O'iiice.V l l Signed and sealed this 12thday ofJanuary A. D. 1937.

Henry van Arsaaie Acting comiasicner' er Patents.

that the said Lettere-Patent ketene, the condensed l (sans CRAWFORD mlLLocx GREENEVALT. 10

by the pyrolysis of acetone. the step which comprises passing pyroiysis gases cooled substantialiy to their dew point thru a reflux condenser counter-current .to a descending ilow oi( condensed acetone whereby to eiIect substantially vapor phase separation oi the acetone from the acetone being maintained substantially at its boiling point to prevent absorption of ketene therein.

3. In the process o! producing ketene by the cmarrnoi'r yel CORRECTION.

Patent No. 240525,286. September 8, 1.936.

CRAWFORD HALLOCK GBEENEWALT It is hereby certifiedtthat error appearsA in the printed specification oi the above-numbered patentrequiring correction as follows: Page 2. second column linel. for ketone read ketene; and i shouldbe read with this correction therein that the same may conform to the record of the .case in' the Patent O'iiice.V l l Signed and sealed this 12thday ofJanuary A. D. 1937.

Henry van Arsaaie Acting comiasicner' er Patents.

that the said Lettere-Patent 

